This invention relates to a mandrel assembly for attaching a portable lathe to the end of a pipe or tube. Portable lathes are well known and are utilized to perform various machining operations on the end of a pipe or tube. The lathe may have a plurality of cutting tools thereon which may face, bevel or perform other machining operations on the pipe end.
The portable lathe is usually supported on a mandrel which may be attached to the interior of the pipe via a radially expandable and contractable clamping device. To ensure the accuracy of the machining operations performed on the end of the pipe, it is of the utmost importance that the mandrel be coincident with the longitudinal axis of the pipe and be rigidly affixed to the pipe. The clamping device typically comprises a plurality of wedge clamping blocks each having a wedge surface thereon which slidably engages a correspondingly tapered surface formed on a mandrel head. Longitudinal movement of the wedge clamping block with respect to the mandrel head causes the diameter defined by the outer surface of the blocks to expand or contract so as to engage or disengage the inner surface of the pipe.
The portable lathe may be utilized on a wide variety of pipe sizes and it is desirable to have the clamping device accommodate as wide a range of pipe sizes as possible. However, heretofore it has been necessary to completely replace the individual wedge clamping blocks to accommodate the wide variety of pipe sizes.
Also, it is imperative that the torque imparted to the mandrel due to the reaction between the rotating cutting head of the portable lathe and its connection to the mardrel be completely reacted by the mandrel and its clamping device. The rather narrow lateral width of the bearing surfaces between the individual clamping wedges and the mandrel head of the prior art devices has not solved this problem, especially where large torque loads are imparted to the mandrel.